Bump rexml from 3.2.8 to 3.3.9

Bumps [rexml](https://github.com/ruby/rexml) from 3.2.8 to 3.3.9.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](ruby/rexml@v3.2.8...v3.3.9)

---
updated-dependencies:
- dependency-name: rexml
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Gemfile.lock

@@ -198,8 +198,7 @@ GEM
     regexp_parser (2.9.0)
     reline (0.5.8)
       io-console (~> 0.5)
-    rexml (3.2.8)
-      strscan (>= 3.0.9)
+    rexml (3.3.9)
     rspec (3.13.0)
       rspec-core (~> 3.13.0)
       rspec-expectations (~> 3.13.0)
@@ -248,7 +247,6 @@ GEM
       lint_roller (~> 1.1)
       rubocop-performance (~> 1.20.2)
     stringio (3.1.0)
-    strscan (3.1.0)
     thor (1.3.1)
     timeout (0.4.1)
     tzinfo (2.0.6)